Also, please make sure that programmatic updates to custom variables trigger style recalculations not only on elements and their children, but their *pseudo*-elements as well. For example, this codepen (http://codepen.io/traviskaufman/pen/jARYOR) does not work in Safari 9.1 because of this problem (fixed in 10 and TP) :)

Please keep the promise of Edge and make a modern browser. Right now, MS IE&Edge is the last one not to implement it. There is a clear set of bonuses and a clear need for it, please implement it! I am saying this as part of a web consulting company, not as a individual.

I use LESS for this. I CAN NOT use a pre-processor because the web-app I have written allows users to write an upload their own css files. Each client is able to create their own template html and LESS formatted css, upload it. Then the application injects the data into their template. The variables are used to wrap their css to prevent collisions with other css running on the site.

I'd love to see this bumped up in priority, we're looking at developing a feature around this, and we're just going to have to tell Edge users its not supported in their browser. Now that all the other browsers are shipping support, Edge should try to get this in sooner.